U.S. patent application number 15/606038 was filed with the patent office on 2017-12-21 for fired heater with heat pipe preheater.
The applicant listed for this patent is ExxonMobil Research and Engineering Company. Invention is credited to Hyungsik Lee, Larry M. Saddler.
Application Number | 20170363288 15/606038 |
Document ID | / |
Family ID | 59054220 |
Filed Date | 2017-12-21 |
United States Patent
Application |
20170363288 |
Kind Code |
A1 |
Lee; Hyungsik ; et
al. |
December 21, 2017 |
FIRED HEATER WITH HEAT PIPE PREHEATER
Abstract
An improved fired heater with air preheating provided by one or
more heat pipes. The fired heater may include at least one burner
for combusting a fuel stream and an air stream and producing heated
exhaust gases; a hot gas flow path and at least one conduit
containing a process fluid to be heated by heat transfer from the
heated exhaust gases; and an air preheater comprising at least one
heat pipe having a first section exposed to the heated exhaust
gases and a second section exposed to the air stream, wherein the
heat pipe is positioned and arranged to transfer heat from the
heated exhaust gases to the air stream, wherein the at least one
heat pipe contains a working fluid sealed within the heat pipe,
wherein said working fluid transfers heat from the heated exhaust
gas to the air stream to be preheated.
Inventors: |
Lee; Hyungsik; (Houston,
TX) ; Saddler; Larry M.; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ExxonMobil Research and Engineering Company |
Annandale |
NJ |
US |
|
|
Family ID: |
59054220 |
Appl. No.: |
15/606038 |
Filed: |
May 26, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62352099 |
Jun 20, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C10G 9/20 20130101; Y02E
20/34 20130101; Y02E 20/348 20130101; F23L 15/045 20130101; C10G
9/005 20130101; F28D 15/0275 20130101; F23L 15/00 20130101; F28D
7/08 20130101; F28D 21/001 20130101 |
International
Class: |
F23L 15/04 20060101
F23L015/04 |
Claims
1. A fired heater comprising: at least one burner for combusting a
fuel stream and an air stream and producing heated exhaust gases; a
hot gas flow path and at least one conduit containing a process
fluid to be heated by heat transfer from the heated exhaust gases;
and an air preheater comprising at least one heat pipe having a
first section exposed to the heated exhaust gases and a second
section exposed to the air stream, wherein the heat pipe is
positioned and arranged to transfer heat from the heated exhaust
gases to the air stream, wherein the at least one heat pipe
contains a working fluid sealed within the heat pipe, wherein said
working fluid transfers heat from the heated exhaust gas to the air
stream to be preheated.
2. The fired heater of claim 1, wherein the air preheater comprises
a plurality of heat pipes.
3. The fired heater of claim 1, wherein the first section of the
heat pipe extends into the hot gas flow path.
4. The fired heater of claim 1, wherein the air preheater includes
a passageway for passage of the heated exhaust gases
therethrough.
5. The fired heater of claim 4, wherein the passageway is
contiguous with a convection section of the fired heater, the
convection section including the at least one conduit containing
the process fluid, and wherein the passageway is fluidly connected
to the hot gas flow path.
6. The fired heater of claim 4, wherein the air preheater provides
a pressure drop of less than 0.8 inch w.c. for a flow velocity of
11 ft/sec through an inlet of the passageway.
7. The fired heater of claim 1, further comprising an exhaust stack
positioned downstream of the convection section, wherein the first
section of the heat pipe is positioned at a same level or above the
conduit of the convection section and below or inside the exhaust
stack.
8. The fired heater of claim 1, wherein the second section of the
heat pipe is elevated relative to the first section of the heat
pipe.
9. The fired heater of claim 8, wherein the heat pipe has a center
axis extending through the first section and second section and the
center axis forms an angle of at least 10 degrees with respect to
the horizon.
10. The fired heater of claim 1, wherein the heated flue gas moves
through the convection section and air preheater solely by natural
draft.
11. The fired heater of claim 1, wherein the air stream is fed
through the air preheater and to the at least one burner solely by
a forced draft fan.
12. The fired heater of claim 10, wherein the air stream is fed
through the air preheater and to the at least one burner solely by
a forced draft fan.
13. The fired heater of claim 1, wherein the fired heater is a
delayed coker.
14. The fired heater of claim 1, wherein the heated exhaust gas
stream is cooled in a tubular air preheater before it passes by the
first section of the heat pipe.
15. A method for operating a fired heater comprising: (a)
combusting a fuel stream and an air stream to produce heated
exhaust gases; (b) exposing the heated exhaust gases to a conduit
transporting a process fluid to be heated by heat transfer from the
heated exhaust gases; (c) exposing the heated exhaust gases to at
least one heat pipe downstream of the conduit; (d) transferring
heat from the heated exhaust gases to a working fluid in the at
least one heat pipe; and (e) transferring heat from the working
fluid to the air stream to preheat the air stream.
16. The method of claim 15, wherein steps (a)-(e) are performed
without the assistance of an induced draft fan.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application relates and claims priority to U.S.
Provisional Application No. 62/352,099, filed on Jun. 20, 2016, the
disclosure of which is incorporated herein specifically by
reference in its entirety.
FIELD
[0002] This invention concerns a fired heater with a heat pipe
preheater.
BACKGROUND
[0003] Air preheaters are used to improve the thermal efficiency of
fired heaters. In a common application, a heat exchanger is used to
transfer heat from the flue gas exiting a fired heater to its
incoming combustion air. Such installations typically require
significant ducting to route flue gas to the location of the heat
exchanger and then to a flue gas stack and additional ducting to
route incoming combustion air from the heat exchanger to the
burners of the fired heater. In addition, forced draft fans are
generally needed to drive the incoming combustion air through the
restrictive heat exchanger and induced draft fans are generally
needed to pull flue gas through the heat exchanger and out the flue
gas stack.
[0004] It would therefore be desirable to provide new air
preheating systems for fired heaters that avoid some of the
drawbacks of existing systems.
SUMMARY
[0005] We have now developed an improved fired heater with air
preheating provided by one or more heat pipes. The fired heater may
include at least one burner for combusting a fuel stream and an air
stream and producing heated exhaust gases; a hot gas flow path and
at least one conduit containing a process fluid to be heated by
heat transfer from the heated exhaust gases; and an air preheater
comprising at least one heat pipe having a first section exposed to
the heated exhaust gases and a second section exposed to the air
stream, wherein the heat pipe is positioned and arranged to
transfer heat from the heated exhaust gases to the air stream,
wherein the at least one heat pipe contains a working fluid sealed
within the heat pipe, wherein said working fluid transfers heat
from the heated exhaust gas to the air stream to be preheated.
[0006] A method is also provided for operating a fired heater. The
method includes combusting a fuel stream and an air stream to
produce heated exhaust gases; exposing the heated exhaust gases to
a conduit transporting a process fluid to be heated by heat
transfer from the heated exhaust gases; and exposing the heated
exhaust gases to at least one heat pipe downstream of the conduit;
transferring heat from the heated exhaust gases to a working fluid
in the at least one heat pipe; and transferring heat from the
working fluid to the air stream to preheat the air stream.
DRAWINGS
[0007] FIG. 1 is a schematic illustrating a fired heater including
a heat pipe preheater according to one or more embodiments of the
present invention.
[0008] FIG. 2 is a detail view illustrating the heat pipe preheater
of the fired heater of FIG. 1.
[0009] FIG. 3 is a detail view illustrating a heat pipe preheater
for a fired heater according to one or more embodiments of the
present invention.
DETAILED DESCRIPTION
[0010] Improved fired heaters are provided which incorporate heat
pipe air preheaters for preheating combustion air. As used herein,
the term "fired heater" refers to a direct-fired heat exchangers
that use heat of combustion to raise the temperature of a material
flowing through one or more coils throughout the heater. The
material flowing through the one or more coils can be any type of
material to be heated, such as a process fluid. For example, the
material can be a feed material for another process, such as feed
for a cracking unit. In some embodiments, the fired heater may be a
furnace for a delayed coker unit and the process fluid may be a
residual oil from a vacuum distillation unit.
[0011] In some embodiments, the improved fired heaters can avoid
one or more of the disadvantages associated with traditional air
preheater heat exchangers. For example, in some embodiments the air
preheater may be contiguous with the convection or radiant section
of the fired heater, thereby avoiding or limiting the ducting
required to direct the heated exhaust gases to the heat exchanger.
In addition, the improved fire heater can utilize one or more heat
pipes that are positioned and arranged to limit the restriction of
flow of the heated exhaust gases or combustion air through the air
preheater. By limiting the pressure drop across the air preheater,
it is possible to provide air preheating without the assistance of
an induced draft fan (e.g., on the heated exhaust gas side of the
preheater). Accordingly, in some embodiments, exhaust gases can
flow unaided by draft fans and entirely by natural draft using the
thermo siphon effect created by combustion of fuel gas at the
burners of the fired heater.
[0012] The improved fired heater can include at least one burner
for combusting a fuel stream and an air stream and producing heated
exhaust gases; a hot gas flow path; at least one conduit containing
a process fluid to be heated by heat transfer from the heated
exhaust gases; and an air preheater comprising at least one heat
pipe having a first section exposed to the heated exhaust gases and
a second section exposed to the air stream. The heat pipe is
positioned and arranged to transfer heat from the heated exhaust
gases to the air stream. The heat pipe contains a working fluid
sealed within the heat pipe, and the working fluid transfers heat
from the heated exhaust gas to the air stream to be preheated.
[0013] In any embodiment, the air preheater can include a plurality
of heat pipes, each having an evaporator section extending into the
hot gas flow path, which passes through a passageway in the air
preheater. The passageway may be contiguous with a convection
section of the fired heater (or the radiant section if the fired
heater does not include a convection section). Each heat pipe also
may include a condensing section extending into a passageway for
receiving a flow of combustion air for the fired heater. The
condensing section of the heat pipe may be elevated relative to the
evaporator section of the heat pipe. For example, the heat pipe may
have a center axis extending through the evaporator section and
condenser section and the center axis may form an angle of at least
10 degrees with respect to the horizon.
[0014] Preferably, the number, size, and arrangement of the heat
pipes in the passageway may be configured to provide a pressure
drop of less than 0.8 inch w.c. (inch water column), more
preferably less than 0.7 inch w.c., more preferably less than 0.6
inch w.c., more preferably less than 0.5 inch w.c., more preferably
less than 0.4 inch w.c., more preferably less than 0.3 inch w.c.,
more preferably less than 0.2 inch w.c., more preferably less than
0.1 inch w.c., more preferably less than 0.05 inch w.c. for a flow
velocity of 11 ft/sec at the flue gas side inlet of the air
preheater.
[0015] Because such little resistance to flow is provided by the
air preheater, heated flue gas may move through the convection
section and air preheater solely by natural draft. Similarly, the
air stream for combustion may be fed through the air preheater
solely by natural draft. In other embodiments, induced draft fans
might also be employed, though it is expected that their demand
would be substantially reduced in comparison to the case where a
conventional heat exchanger is employed for the air preheater. For
example, in any embodiment an induced draft fan, providing a motive
pressure of less than 0.8 inch w.c., such as less than 0.5 inch
w.c., or less than 0.1 inch w.c., can be employed between the air
preheater and flue gas stack. Further, in some embodiments, the
heated exhaust gas stream may be cooled in a tubular air preheater
before it contacts the heat pipes of the air preheater.
[0016] In any embodiment, operating velocity for the flue gas
through the inlet of flue gas side of the preheater may be 0.1 to
25 ft/sec, but is preferably in the range of 0.1 to 15 ft/sec, and
even more preferably between 0.1 to 11 ft/sec, or 1 to 11 ft/sec,
or 2 to 11 ft/sec, or 3 to 11 ft/sec. or 4 to 11 ft/sec, or 5 to 11
ft/sec.
[0017] The improved fired heater may further include an exhaust
stack positioned downstream of the convection section. In some
embodiments, the exhaust stack may be in substantial vertical
alignment with the convection and/or radiant sections of the fired
heater as well as the passageway of the air preheater containing
the evaporator sections of the heat pipes. The evaporator sections
of the heat pipe may be positioned at a same level or above the
conduit containing the process fluid of the convection section and
below or inside the exhaust stack.
[0018] An exemplary embodiment is illustrated in FIG. 1. Fired
heater 10 includes air preheater 12, having a plurality of heat
pipes 28, which preheats ambient combustion air before it passes
through ducting 14 to burners 16 where the combustion air and a
fuel are ignited. Heat produced from the combustion of the air and
fuel heats radiant coil 20, and the process fluid passing
therethrough, in radiant section 18. The heated exhaust gases pass
through convection section 22 where the gases heat convection coil
24 and the fluid passing therethrough. The fluid heated in
convection coil 24 may be the same or different fluid than the
process fluid heated in radiant coil 20.
[0019] The heated exhaust gases then pass through passageway 26 of
the air preheater 12 where sections of the heat pipes 28 extending
into passageway 26 are heated. This heat is then transferred to
other sections of the heat pipes 28 which heat the combustion air
passing through air preheater 12. The heated exhaust gases then
pass through stack 30 before they are released into the
atmosphere.
[0020] As illustrated in FIG. 1, air preheater 12 may be contiguous
to the convection section 22 of the fired heater (or it may be
contiguous with the radiant section 18 in cases where the fired
heater does not include a separate convection section). This avoids
the need for additional ducting of the exhaust gas to a heat
exchanger placed in a different location on the ground plot. The
heat pipe air preheater 12 may be sufficiently small and
lightweight to be secured directly to the fired heater 10 between
the fired heater 10 and the stack 30 (i.e., the heat pipes may be
disposed in a heated exhaust gas passageway 26 that is in
substantial vertical alignment with the convection section 22 or
radiant section 18 and also in substantial vertical alignment with
stack 30).
[0021] The air preheater 12 of FIG. 1 is shown in greater detail in
FIG. 2. The air preheater 12 generally includes a plurality of heat
pipes 28 that have first sections that extend into heated exhaust
gas passageway 26 and second sections that extend into combustion
air passageway 32. Each heat pipe 28 is partly filled with a
working fluid, such as water or a hydrocarbon, and is sealed. The
heated exhaust gas passing through passageway 26 transfer heat to
the evaporator sections of the heat pipes 28 to evaporate the
working fluid and the heated vapor flows to the other, condenser
end, where it gives up heat to the incoming combustion air flowing
over the condenser sections of the heat pipes 28. The condenser
ends are elevated related to the evaporator ends so that condensed
working fluid flows back under gravity to the evaporator ends. The
condenser ends are preferably elevated by 10 degrees or more than
the condenser ends (i.e., the heat pipe has a center axis extending
through the first section and second section and the center axis
forms an angle of at least 10 degrees with respect to the
horizon).
[0022] Each heat pipe 28 generally includes an outer container and
a working fluid contained therein. The outer container isolates the
working fluid from the heated exhaust gases and the combustion air.
The container preferably may be made of carbon steel. Passageway 26
and passageway 32 are also separated by a divider (tube sheet) or
other structure to maintain physical separation between the flue
gases and the combustion air.
[0023] The working fluid within the heat pipe 28 is selected to
have a vapor temperature range appropriate to the intended
operations. The vapor pressure over the operating temperature range
should be sufficiently great to avoid high vapor velocities, which
can cause flow instabilities. The fluid should exhibit good thermal
stability, a vapor pressure not too high or low over the
temperature range, a high latent heat, high thermal conductivity,
low liquid and vapor viscosities, and acceptable freezing or pour
point. The selection should also be based on thermodynamic
considerations which are concerned with the various limitations to
heat flow occurring within the heat pipe such as viscous, sonic,
capillary, entrainment and nucleate boiling levels. While a wicking
material is not required with pipe positions that are disclosed
herein, it is not excluded.
[0024] Exemplary working fluids include acetone and other ethers,
alcohols such as ethanol, methanol, propanol, and butanol,
hydrocarbons, such as toluene, perhalocarbons, naphthalene,
Dowtherm.TM. heat transfer fluids and water. Mercury may be
suitable, but may be unpreferred for environmental reasons. Liquid
metals such as sodium, lithium and sodium/potassium alloy may be
useful in high temperature applications but are not usually
required in the present applications.
[0025] In any embodiment the air preheater may include additional
features to improve performance of the preheater. For example, the
air preheater may include a tubular heat exchanger upstream of the
heat tubes, which may be helpful in some cases to further cool the
heated exhaust gases before they are exposed to the heat tubes. As
illustrated in FIG. 3, combustion air may be fed through the
interior of tubular heat exchanger 42 via manifold 40. Heat from
the heated exhaust gases is transferred to the air through the heat
exchanger 42 so that the heated exhaust gases passing through
passageway 48 is cooled prior to transferring heat to heat pipes
46. The combustion air enters into passageway 44 where it is then
further heated by heat pipes 46. Such a configuration may be
particularly useful in cases where the temperature of the heated
exhaust gases would cause the heat pipes 46 to exceed the critical
temperature of the working fluid or would otherwise cause the heat
pipes 46 to operate outside of their ideal range. The heat pipes
can include various features to improve heat transfer to or from
the heat pipes, such as fins or other heat-transferring
elements.
[0026] The following embodiments are also provided:
Embodiment 1
[0027] A fired heater comprising: at least one burner for
combusting a fuel stream and an air stream and producing heated
exhaust gases; a hot gas flow path and at least one conduit
containing a process fluid to be heated by heat transfer from the
heated exhaust gases; and an air preheater comprising at least one
heat pipe having a first section exposed to the heated exhaust
gases and a second section exposed to the air stream, wherein the
heat pipe is positioned and arranged to transfer heat from the
heated exhaust gases to the air stream, wherein the at least one
heat pipe contains a working fluid sealed within the heat pipe,
wherein said working fluid transfers heat from the heated exhaust
gas to the air stream to be preheated.
Embodiment 2
[0028] The fired heater or method of any other Embodiment, wherein
the air preheater comprises a plurality of heat pipes.
Embodiment 3
[0029] The fired heater or method of any other Embodiment, wherein
the first section of the heat pipe extends into the hot gas flow
path.
Embodiment 4
[0030] The fired heater or method of any other Embodiment, wherein
the air preheater includes a passageway for passage of the heated
exhaust gases therethrough.
Embodiment 5
[0031] The fired heater or method of any other Embodiment, wherein
the passageway is contiguous with a convection section of the fired
heater, the convection section including the at least one conduit
containing the process fluid, and wherein the passageway is fluidly
connected to the hot gas flow path.
Embodiment 6
[0032] The fired heater or method of any other Embodiment, wherein
the air preheater provides a pressure drop of less than 0.8 inch
w.c. for a flow velocity of 11 ft/sec through an inlet of the
passageway.
Embodiment 7
[0033] The fired heater or method of any other Embodiment, further
comprising an exhaust stack positioned downstream of the convection
section, wherein the first section of the heat pipe is positioned
at a same level or above the conduit of the convection section and
below or inside the exhaust stack.
Embodiment 8
[0034] The fired heater or method of any other Embodiment, wherein
the second section of the heat pipe is elevated relative to the
first section of the heat pipe.
Embodiment 9
[0035] The fired heater or method of any other Embodiment, wherein
the heat pipe has a center axis extending through the first section
and second section and the center axis forms an angle of at least
10 degrees with respect to the horizon.
Embodiment 10
[0036] The fired heater or method of any other Embodiment, wherein
the heated flue gas moves through the convection section and air
preheater solely by natural draft.
Embodiment 11
[0037] The fired heater or method of any other Embodiment, wherein
the air stream is fed through the air preheater and to the at least
one burner solely by a forced draft fan.
Embodiment 12
[0038] The fired heater or method of any other Embodiment, wherein
the air stream is fed through the air preheater and to the at least
one burner solely by a forced draft fan.
Embodiment 13
[0039] The fired heater or method of any other Embodiment, wherein
the fired heater is a delayed coker.
Embodiment 14
[0040] The fired heater or method of any other Embodiment, wherein
the heated exhaust gas stream is cooled in a tubular air preheater
before it passes by the first section of the heat pipe.
Embodiment 15
[0041] A method for operating a fired heater comprising: (a)
combusting a fuel stream and an air stream to produce heated
exhaust gases; (b) exposing the heated exhaust gases to a conduit
transporting a process fluid to be heated by heat transfer from the
heated exhaust gases; and (c) exposing the heated exhaust gases to
at least one heat pipe downstream of the conduit; (d) transferring
heat from the heated exhaust gases to a working fluid in the at
least one heat pipe; and (e) transferring heat from the working
fluid to the air stream to preheat the air stream.
Embodiment 16
[0042] The method of Embodiment 15, wherein steps (a)-(e) are
performed without the assistance of an induced draft fan.
* * * * *